Fix #2099.

CHANGELOG.md

@@ -32,6 +32,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 * A crash in alias checking under some rare circumstances (#2096).
 
+* Mishandling of existential sizes for top level constants. (#2099)
+
 ## [0.25.12]
 
 ### Added

src/Futhark/Internalise/Exps.hs

@@ -58,6 +58,9 @@ internaliseValBind types fb@(E.ValBind entry fname _ (Info rettype) tparams para
         first zeroExts . unzip . internaliseReturnType (map (fmap paramDeclType) all_params) rettype
           <$> mapM subExpType body_res
 
+      when (null params') $
+        bindExtSizes (E.AppRes (E.toStruct $ E.retType rettype) (E.retDims rettype)) body_res
+
       body_res' <-
         ensureResultExtShape msg loc (map I.fromDecl rettype') $ subExpsRes body_res
       let num_ctx = length (shapeContext rettype')

tests/issue2099.fut

@@ -0,0 +1,6 @@
+-- ==
+-- input {}
+-- output { [100, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 11i64 }
+
+def numbers = concat [100] (0..<10i32)
+entry main = (numbers, length numbers)